var banner = new Array();

banner.push('http://img16.imageshack.us/img16/7237/mieuxca2011.png');
banner.push('http://i28.servimg.com/u/f28/12/68/76/57/banier13.jpg');
banner.push('http://i28.servimg.com/u/f28/12/68/76/57/banier16.jpg');

document.getElementById('logo').firstChild.src= banner[Math.floor(Math.random()*banner.length)];

setInterval("document.getElementById('logo').firstChild.src= banner[Math.floor(Math.random()*banner.length)];",5000);